1. Field of the Invention
The invention relates to the fields of disk drive operation and audio storage/playback, and in particular to controlling the operating speed of a disk drive when storing or retrieving data and choosing a disk location for storing the data, the choice of speed and disk location being based on the type of data being stored or retrieved, and the type of operation the retrieved data is used for, e.g., audio playback.
2. Background Information
Many modern electrical devices store and read data. For example, compact disk players read digitized audio data from a plastic disk storage medium with a laser. A video cassette recorder stores and reads audio and video data using magnetic tape as a storage medium. Computer systems are designed to read and store large amounts of data. A computer system will typically employ several types of storage devices, each used to store particular kinds of data for particular computational purposes. Electronic devices may use programmable read-only memory (PROM), random access memory (RAM), flash memory, magnetic tape or optical disks as storage medium components, but many devices, especially computers, store data in a direct access storage device (DASD) such as a hard disk drive.
Although such data storage is not limited to a particular direct access storage device, one will be described by way of example. A hard disk drive typically includes one or more circular magnetic disks as the storage media which are mounted on a spindle. The disks are spaced apart so that the separated disks do not touch each other. The spindle is attached to a motor which rotates the spindle and the disks, normally at a relatively high revolution rate, e.g., 5400 rpm. A disk controller activates the motor and controls the read and write processes which will now be described.
Storage of data on a magnetic disk storage medium entails magnetizing portions of the disk in a pattern which represents the data. In order to write the data onto the magnetic surface of the disk, a small generally ceramic block called a xe2x80x9csliderxe2x80x9d which contains a magnetic transducer is positioned over the traveling surface of the rotating disk. This transducer is also known as a write element or write head. The write element is typically xe2x80x9cflownxe2x80x9d at a height of approximately six millionths of an inch from the surface of the spinning disk.
Generally, before storing user data, the disk is formatted (also using the write head) so that its surface is organized into a series of identifiable locations on concentric tracks, according to known methods. As will be described later, the tracks may be further organized into groups of tracks forming a plurality of recording xe2x80x9czones.xe2x80x9d When a designated track location on the disk surface is under the write element, the write element is energized to various states by the disk controller, causing the track location below to be magnetized in a way representing the user data to be stored.
Reading recorded data from a magnetized disk is accomplished in a similar fashion. When a read element or read head is flown over the spinning disk, a signal is induced in the read element as it passes over previously magnetized portions of the disk where data has been recorded. To perform a read operation, the disk controller determines the location of the desired recorded data, moves the read head to that location, and captures a signal induced in the read element by the traveling disk when the read element is above the specified location. This induced signal corresponding to the originally recorded data is subsequently processed and the original data reconstructed from the signal induced in the read element. In some devices, the write element also acts as the read element while in others, separate and distinct write and read elements are used. These elements may be disposed on the same head assembly or separate head assemblies.
Generally, each of the head assemblies having the read/write elements of a disk drive are held and positioned by an actuator arm attached to a stepper motor which is directed by the disk drive controller to move the respective head assembly across the radius of the rotating disk from track to track. The elements must be controlled precisely so that the desired user data location is accurately found on the disk.
Further, serious malfunctions, including data loss and physical damage to the disk surface and/or read/write elements, can result if the read/write elements come in contact with data containing portions of the surface of the magnetic disk, especially while it is rotating at high speeds. Generally, a xe2x80x9clanding zone,xe2x80x9d an area on the disk surface where no data will be written, is provided for the read/write elements to rest on when the disk device is powered down.
The use of disk drives in such devices as portable computers, personal digital assistants and cellular telephones, for example, has increased significantly over the past several years. Devices of this nature typically have a portable battery pack which provides power to the various components of the device when used away from a power outlet. It is important that the battery pack used to supply power to portable devices be compact and lightweight.
However, as portable devices are increasingly used in locations where an external power source is unavailable, for example, traveling on an airplane, it is also increasingly important that the portable devices operate for significant periods of time between recharging of the battery pack. Bigger batteries tend to provide longer use time however they increase the weight of the device. Hence, the desire to achieve a compact and light weight design often competes with a desire for longer usage time of the portable device between charging the battery pack.
In order to increase operating time in portable devices, various steps have been taken to reduce the power consumption of components used in the devices. Moreover, increased efforts have also been made to reduce power consumption in fixed devices, like desk-top computers, in order to more generally conserve energy resources. The Environmental Protection Agency (EPA) now provides for power saving status to be granted to computers meeting certain standards.
Thus, efforts to reduce power consumption of the various components of a computer have been increasingly employed. For example, the central processing unit (CPU) often includes some form of power management function to reduce clock frequency of the CPU when the computer enters a power saving mode, and may act to place various components into a sleep mode where reduced power is used. In general, a power saving mode may be invoked to reduce use of power by a component of the computer when the component is not being used.
In the case of memory storage devices, various power saving techniques have been employed. For example, in disk drives, the spindle motor which rotates the disk storage media uses a large percentage of the total power of the disk drive. In order to conserve power, it has been proposed that the spindle speed of the disk drive be reduced or stopped when the disk drive is not being used. As will be discussed later, depending on head design, reducing spindle speed can adversely affect disk drive reliability if adequate precautions are not taken.
In a typical approach, a normal operating spindle velocity is used by the disk drive during read and write operations to the disk. When the power saving mode is initiated, for example when the disk drive is not accessed for a predetermined period of time, the spindle velocity of the disk is reduced or stopped to conserve power. When an access operation to the disk drive is initiated, the spindle speed is increased until the disk is rotated at the normal operating velocity prior to beginning the read or write operation. In other words, the power saving mode is disengaged and the disk brought up to operational RPM prior to commencement of read and write operations.
A further known technique for conserving storage device power is to use the lightest/smallest possible storage medium, e.g., disks. However, this results in an increased total storage requirement, overall storage density, for the disk. One technique used to achieve the increased storage is called zone bit recording (ZBR). With a constant disk velocity measured in RPM, the linear speed of the disk as it moves past the transducer (head) varies with the diameter of the disk. The linear velocity is, of course, higher at outer diameters than at inner diameters of the disk, since the circumference of the disk increases with the diameter. The length of the concentric tracks increases with diameter.
ZBR takes advantage of this property by dividing the disk surface into a plurality of zones based on diameter, and increasing the frequency in a particular zone at which data is recorded to the disk, from an inner diameter zone to an outer diameter zone. This increases the linear density (bits per unit length) of the recorded data in each zone so that it approaches a maximum density limit for the particular disk media used. The maximum density limit depends primarily on the physical properties of type of medium material used.
Thus, with ZBR, the total storage is increased over the case where the disk is essentially one zone and none of the increased density potential of the outer diameters is utilized.
U.S. Pat. No. 5,787,292, describes a multiple frequency zoned disk storage device, in which data is further read from and/or written to the disk at two or more discrete disk velocities. A low power mode is described where information is read/written from/to the disk while the disk velocity is reduced to conserve power. An embodiment of the described device incorporates zone bit recording such that when one of the different disk motor speeds is used for write operations, an appropriate write frequency for a particular zone is selected such that the linear density approaches the maximum possible for the media used. In other words, the disk rotation speed adjustment for low power mode is factored into the selection of the write frequency for a particular zone.
The patent also describes an activity monitor which detects requests for disk read/write activity, and can cause the disk spindle motor speed to be reduced to conserve energy after a certain period of inactivity. However, because the disk, spindle and motor all have mass, the speed cannot be changed instantaneously. Therefore, in order to reduce any waiting time while changing speeds, the patent further provides that if a high disk activity is anticipated (by a host computer, for example) for future operations, the spindle speed may be increased prior to initiation of such activity.
According to the particular type of activity anticipated, it is determined what level of disk activity will be required, e.g., very high, high, medium high, average, etc. For example, data base search operations or those heavily using graphics require relatively high disk activity. An appropriate disk controller operating frequency for the type of disk activity level can thereby be selected.
Further according to that patent, the activity monitor may also receive (from the host computer, for example) an indication of the type of data to be read from or written to the disk, and may use this indication to ensure that a satisfactory spindle speed is used for the type of information being read.
However, because of the continuing need for power conservation, further disk drive operation improvements would be useful and beneficial.
It is, therefore, a principle object of this invention to provide a method and apparatus for adaptive disk drive operation.
It is another object of the invention to provide a method and apparatus that solves the above mentioned problems so that disk drive power consumption and operation is further optimized.
These and other objects of the present invention are accomplished by the method and apparatus disclosed herein.
It should be noted that this invention is not limited to use in disk drives using magnetic media but is useful in any device having rotating or otherwise traveling media. In this particular application, where magnetic media is described as an example, it should be recognized that the invention would be useful in other storage devices which have different types of media or read and write elements.
When considering the above mentioned problems and needs for energy conservation, Applicant recognized that there is a lower data rate requirement for some kinds playback, and that the electrical power requirements of a hard disk drive could be reduced in those types of playbacks by reducing the rotational speed of the disks. For example, audio data, like phonemail or text messages, is relatively less data rate intensive than video data. That is, audio data can be played back audibly even though retrieved at a relatively low rate. Of course, the required effective rate of data retrieval depends on the way the data will be used. An audio file could be retrieved slowly for listening, but might require faster retrieval when being input into a spectral analysis program for processing, for example. Therefore, the way the data will be used also determines the xe2x80x9ctypexe2x80x9d of data, for the purposes of selecting a required disk speed.
Applicant further recognized that altering the disk rotational speed could adversely affect the reliability of the drive unless suitable precautions are taken. For example, some drives are designed such that the flying height of the slider having the read and write elements changes when the speed of the disk changes. Advantageously, according to an aspect of the invention, the flying height of the slider is taken into account, along with the type of data being stored/retrieved from the disk, when reducing disk rotational speed to reduce power. The disk rotation speed is chosen accordingly, thereby avoiding any significant threats to disk drive reliability.
According to an aspect of the invention, the invention uses multiple disk speeds, which can be measured in revolutions per minute (RPM) and in terms of the linear (traveling) speed of the disk surface with respect to the read/write element, to maintain an adequate data rate while simultaneously reducing power consumption in hard disk drives. For example, phonemail can be received over a network at a high data rate and in a short period of time. However, when played back, the data rate can be significantly reduced because the data rate need only be high enough to support whatever audio decompression and digital-to-analog conversion is required to reproduce audio frequencies for listening.
According to another aspect of the invention, the particular instantaneous disk RPM being used for low speed operation can advantageously be adjusted when other demands are made on the disk drive. For example, if while listening to phonemail using a reduced disk RPM, new data which must be stored is received, the phonemail playback may be interrupted and the disk RPM increased to accommodate immediate storage of the new data at the standard disk RPM. Alternatively, according to another aspect the invention, this can be accomplished without interrupting phonemail playback by buffering either the new data or the phonemail. The new data could be buffered while the phonemail is played at the lower disk speed, and subsequently stored at the standard disk speed (RPM) after the phonemail playback is completed, for example. Alternatively, the disk speed could be increased to the standard disk speed, the as yet unplayed phonemail could be read into a buffer at the standard disk speed, and then the buffered phonemail played back from the buffer while the new data is being written to the disk at the standard disk speed.
According to another aspect of the invention, the location for the phonemail or other audio-type data that can use a lower data rate for playback is optimized so that at low disk RPM, a slider-to-disk distance, which can affect disk drive reliability, is not adversely affected.
According to another aspect of the invention, the invention does not preclude increasing the disk RPM for playback if needed for a particular application, for example, where the data being played back is video and a higher data rate may be required as compared with purely audio playback.
According to another aspect of the invention, phonemail can advantageously be saved on the disk drive at low disk RPM, which significantly reduces the power consumed by the disk drive, especially for long messages.
According to another aspect of the invention, phonemail is advantageously retrieved from the disk drive at low disk RPM which significantly reduces the power consumed by the disk drive, especially for long messages.
According to another aspect of the invention, different disk rotation speeds are advantageously used when recording and playing back certain audio information. This can be very useful for cellular phones, personal digital assistants (PDA), and other portable devices that rely on battery power, for example.
In a particular advantageous use in accordance with the above aspect of the invention, consider a cellular phone or PDA with an internal hard drive. Phonemail messages are received by the PDA and stored on the hard drive at the normal data rate and disk speed. The network phonemail is probably compressed and encrypted. A one minute phonemail message can be stored on the drive in a few seconds at most. Later, when the phone messages are played back, since the required data rate when listening to phonemail is lower, and might be only 1/100 of that used to store the messages, to conserve disk drive power, the disk speed (RPM) can be advantageously lowered. According to this aspect of the invention, the hard drive uses its maximum data rate and disk speed only when storing the network phonemail.
These and other aspects of the invention will become apparent from the detailed description set forth below.